The city of Perugia did not like this cheating (imagine the hot arguments  between the vendors and the sellers) and introduced three fixed lengths: they are long 97, 63, and 41 cm, respectively.  They can be neither shortened  nor prolonged as you can see. They are engraved on the facade of the Palace of the Captain of the People (namely the house of the major in the medieval times) that at present is a court house...  

Chiara and Agnese are showing you the three lengths. The two girls are your guides of the Perugia Street Math. They are two senior math students at the University of Perugia.

Just to give you a glimpse of the confusion that may ensued by having different length measures, read the following excerpt from this famous 1744 book  by Euler:

where a Rhenanian foot (pedes in Latin) is cited (10th line) as a measurement of length:

This book (E65) can be downloaded for free at the online Euler Archive:

www.eulerarchive.org

Actually the full-color scan of an original copy of E65 is available at the website of the Posner Memorial Collection, located at the Carnegie Mellon Library in USA.

If you wants to have an idea of the many measurements that were/are adopted,  look online at  A Dictionary of Units of Measurement
© Russ Rowlett and the University of North Carolina at Chapel Hill, USA

http://www.unc.edu/~rowlett/units/index.html

 There you can find the word Rheinfuss (Rhenian pedes)... 

What is your foot length? Could you find your right shoe size if the foot lengths were different from town to town? 

Think about it: we have still different shoe sizes in USA, UK, Italy, Japan, etc...

See this online Worldwide shoe size conversion table at

www.runtheplanet.com/resources/tools/shoesizeconversion.asp